• 한국대기환경학회지
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• 제15권6호
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• pp.757-765
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• 1999

Lagrangian particle dispersion model(LPDM) is an effective tool to calculate the dispersion from a point source since it dose not induce numerical diffusion errors in solving the pollutant dispersion equation. Fictitious particles are released to the atmosphere from the emission source and they are then transported by the mean velocity and diffused by the turbulent eddy motion in the LPDM. The concentration distribution from the dispersed particles in the calculation domain are finally estimated by applying a particle count method or a Gaussian kernel method. The two methods for calculating concentration profiles were compared each other and tested against the analytic solution and the tracer experiment to find the strength and weakness of each method and to choose computationally time saving method for the LPDM. The calculated concentrations from the particle count method was heavily dependent on the number of the particles released at the emission source. It requires lots fo particle emission to reach the converged concentration field. And resulting concentrations were also dependent on the size of numerical grid. The concentration field by the Gaussian kernel method, however, converged with a low particle emission rate at the source and was in good agreement with the analytic solution and the tracer experiment. The results showed that Gaussian kernel method was more effective method to calculate the concentrations in the LPDM.

• Environmental Sciences Bulletin of The Korean Environmental Sciences Society
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• 제4권2호
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• pp.117-125
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• 2000

A series of simulations were carried out to test the accuracy of a CFD (Computational Fluid Dynamics) model for flow and dispersion problems around buildings. The basic equations involved are Reynolds-averaged Navier-Stokes equations. Two different cases were selected to estimate the accuracy of a CFD model. Case 1 adopted Euler equations, which are obtained by neglecting the viscous fluxes, which can be closed by the $textsc{k}$-$\varepsilon$model for a turbulent close problem. The results of both cases were compared with wind tunnel data. The results for Case 2 were closer to the wind both cases were compared with wind tunnel data. The results for Case 2 were closer to the wind tunnel data than Case 1. Accordingly, this indicates that the inclusion of viscous fluxes in a CFD model is required for the simulation of flow and 야spersion around buildings.

• 한국전산유체공학회지
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• 제6권4호
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• pp.1-7
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• 2001

Wind flow perturbations, recirculations and turbulence generated by buildings often dominate air pollutant distributions around buildings. This paper describes dispersion of contaminants in the vicinity of a building by solving the concentration equation based on previously simulated wind flow field. Turbulence closure is achieved by using the standard k-ε two-equation model. The paper shows application of the CIP method for solving a species concentration equation of contaminant gas around a rectangular building for two different sources under conditions of neutral atmospheric stratification. Results have been compared to the experimental data and the previous numerical results by hybrid scheme. The computational results of concentration profiles by the CIP method agree well with experimental data.

• 한국전산유체공학회지
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• 제3권1호
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• pp.63-72
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• 1998

The numerical simulations of flowfield and pollutant dispersion over two-dimensional hills of various shapes are described. The Reynolds-averaged Wavier-Stokes equations and concentration diffusion equation based on the gradient diffusion theory have been applied to the atmospheric shear flow over the bell-shaped hills which are basic components of the complex terrain. The flow characteristics such as velocity profiles of the geophysical boundary layer, speed-up phenomena, mean pollutant concentration profiles are compared with experimental data to validate the present numerical procedure and it has been found that the present numerical results agree well with experiments and other numerical data. It has been also found that the distributions of ground level concentration are strongly influenced by the source location and height.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집B
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• pp.723-728
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• 2001

Wind flow perturbations, recirculations and turbulence generated by buildings often dominate air pollutant distributions around buildings. This paper describes dispersion of contaminants in the vicinity of a building by solving the concentration equation based on previously simulated wind flow field. Turbulence closure is achieved by using the standard k-e two-equation model. The paper shows application of the CIP method for solving a species concentration equation of contaminant gas around a rectangular building for two different sources under conditions of neutral atmospheric stratification. Results have been compared to the experimental data and the previous numerical results by hybrid scheme. The computational results of concentration profiles by the CIP method agree well with experimental data.

• 대한기계학회논문집B
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• 제35권2호
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• pp.169-178
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• 2011

격자볼츠만 방법(LBM)을 이용하여 난류 경계층에서의 오염물질 확산에 대하여 수치계산을 수행 하였다. 난류 경계층 내의 유동을 모사하기 위하여 격자볼츠만 방법에 Smagorinsky 아격자 모델을 적용한 LB-SGS 모델을 사용하였으며, 오염물질의 확산을 모사하기 위하여 Passive-scalar 방법을 적용하였다. LB-SGS 모델의 신뢰성 검증을 위하여 Fackrell & Robins(1982)과 Raupach & Legg(1983)의 실험 조건과 동일한 조건하에서 수치계산을 수행하였고, 수치계산으로 얻어진 농도 분포를 실험값과 비교하였다. 이 결과로부터 LB-SGS 모델이 난류 경계층 내에서의 오염물질의 농도분포를 예측하는데 적합한 모델임을 알 수 있었다.

• 한국안전학회지
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• 제37권2호
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• pp.1-9
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• 2022

Most factories deal with toxic or flammable chemicals in their industrial processes. These hazardous substances pose a risk of leakage due to accidents, such as fire and explosion. In the event of chemical release, massive casualties and property damage can result; hence, quantitative risk prediction and assessment are necessary. Several methods are available for evaluating chemical dispersion in the atmosphere, and most analyses are considered neutral in dispersion models and under far-field wind condition. The foregoing assumption renders a model valid only after a considerable time has elapsed from the moment chemicals are released or dispersed from a source. Hence, an initial dispersion model is required to assess risk quantitatively and predict the extent of damage because the most dangerous locations are those near a leak source. In this study, the dispersion model for initial consequence analysis was developed with three-dimensional unsteady advective diffusion equation. In this expression, instantaneous leakage is assumed as a puff, and wind velocity is considered as a coordinate transform in the solution. To minimize the buoyant force, ethane is used as leaked fuel, and two different diffusion coefficients are introduced. The calculated concentration field with a molecular diffusion coefficient shows a moving circular iso-line in the horizontal plane. The maximum concentration decreases as time progresses and distance increases. In the case of using a coefficient for turbulent diffusion, the dispersion along the wind velocity direction is enhanced, and an elliptic iso-contour line is found. The result yielded by a widely used commercial program, ALOHA, was compared with the end point of the lower explosion limit. In the future, we plan to build a more accurate and general initial risk assessment model by considering the turbulence diffusion and buoyancy effect on dispersion.

• 해양환경안전학회지
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• 제5권1호
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• pp.9-18
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• 1999

To predict the oil spill dispersion phenomena in the ocean, the oil spill response model, which can be used for strategic purpose on the oil spill site, based on Lagrangian particle-tracking method was formulated and applied to the neighboring area with Pusan port where the oil spill incident occurred when the tanker ship No.1 Youil struck on a small rock near the Namhyungjeto on September 21, 1995. The real-time tidal currents to be required as input data of the oil spill model were obtained by the two-dimensional hydrodynamic model and the tide prediction model. Evaluation of tidal currents using observation data was successful. For wind data, other input data of oil spill model, observed data on the spot were used. To verify the oil spill model, the oil spill modelling results were compared with the field data obtained from the spill site. Compared the modelling results with the observation data, there exist some discrepancies but the general pattern of modelling results was similar to that of field observation. The modelling results on 7 days after spill occurred showed that the 40% of spilled oil is in floating, 36% in evaporated, 23% at shore, and 1% in out of boundary, respectively. According to the evaluation of weighting curves of effective components to the dispersion of oil, the winds make a 37% of contribution to the dispersion of oil, turbulent diffusion 39.5%, and tidal currents 23.5%, respectively. Provided the more accurate wind data are supported, more favorable results might be obtained.

• Asian Journal of Atmospheric Environment
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• 제10권3호
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• pp.125-136
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• 2016

In this study, the effects of the mesh barrier on the free dispersion of ammonia were numerically investigated under different atmospheric conditions. This study presents the detail and flow feature of the dispersion of ammonia through the mesh barrier on various free stream conditions to decline and limit the toxic danger of the ammonia. It is assumed that the dispersion of the ammonia occurred through the leakage in the pipeline. Parametric studies were conducted on the performance of the mesh barrier by using the Reynolds-averaged Navier-Stokes equations with realizable k-${\varepsilon}$ turbulence model. Numerical simulations of ammonia dispersion in the presence of mesh barrier revealed significant results in a fully turbulent free stream condition. The results clearly show that the flow behavior was found to be a direct result of mesh size and ammonia dispersion is highly influenced by these changes in flow patterns in downstream. In fact, the flow regime becomes laminar as flow passes through mesh barrier. According to the results, the mesh barrier decreased the maximum concentration of the ammonia gas and limited the risk zone (more than 500 ppm) lower than 2 m height. Furthermore, a significant reduction occurs in the slope of the upper boundary of $NH_3$ risk zone distribution at downstream when a mesh barrier is presented. Thus, this device highly restricts the leak distribution of ammonia in the industrial plan.

• 대한환경공학회지
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• 제22권7호
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• pp.1173-1182
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• 2000

지금까지 급속혼화는 정수처리 공정 중에서 매우 중요한 공정으로 인식되어 왔다. 특히, 응집제의 원수내 확산은 급속혼화 공정에 이어지는 flocculation이나 filtration 공정에 지대한 영향을 미치게 되므로 지금까지 많은 연구자들이 혼화장치의 개발이나 효율적인 혼화방식에 관해 연구를 해왔다. 그러나 선행 연구자들은 급속혼화에 있어서 중요한 변수로 응집제 주입량, pH, 임펠러의 회전속도, 그리고 G값만을 고려하였으나, 실제 응집제와 콜로이드입자와의 충돌기회에 지대한 영향을 미치는 급속혼화 공정상에서 발생되는 난류장을 간과하였다. 특히 급속혼화에서의 난류의 발생은 G값에 전적으로 의지하여 난류장의 평균값으로 혼화조내의 난류를 표현하여 왔으며, 혼화조의 형상에 따라 달라지는 난류장 해석은 연구가 미약한 실정이다. 이에 본 연구는 급속혼화에서 난류장 해석의 중요성을 인식하고 혼화조의 형상 변화에 따라 달라지는 난류장을 전산유체 프로그램을 통하여 해석하였다. 그리고 혼화조 형상을 달리하며 jar-test를 수행한 결과 배플이 없는 원형 jar의 경우가 배플이 장착된 원형 jar나 Hudson jar보다 응집제의 확산에 따른 탁도 제거효율이 좋은 것으로 나타났으며, 전산유체 프로그램을 이용하여 각각 모사한 결과 벽면효과나 사류지역의 발생 등으로 배플이 없는 원형 jar가 혼화에 효과적인 난류장이 분포되는 것으로 확인되었다. 이 결과를 통해 혼화조 형상이 응집제의 확산이나 난류장의 발생에 영향을 미치는 것으로 결론 내릴 수 있다.